J. Phys. II France
Volume 4, Numéro 1, January 1994
Page(s) 37 - 58
DOI: 10.1051/jp2:1994114
J. Phys. II France 4 (1994) 37-58

Polymerization of a diacetylenic phospholipid monolayer at the air-water interface

L. Bourdieu1, D. Chatenay1, J. Daillant2 and D. Luzet2

1  Institut Curie, Section de Physique et Chimie, Laboratoire de Physico-chimie des Surfaces et Interfaces unité associée CNRS 1379, 11 rue Pierre et Marie Curie, 75005 Paris, France
2  Service de Physique de l'Etat Condensé, Orme des Merisiers, Centre d'études de Saclay, 91191 Gif-sur-Yvette Cedex, France

(Received 20 July 1993, received in final form 17 September 1993, accepted 23 September 1993)

Monolayers of a polymerizable phospholipid on water have been studied both before and after polymerization. Before polymerization, the phase diagram is established by isotherm measurements and optical microscopy (epifluorescence and direct observation between crossed polarizer and analyzer). This allows us to bring into evidence a coexistence region between a condensed and an expanded phase, above a triple point temperature $T_{\rm t} = 20~^{\circ}$C. The dramatic influence of impurities on the size of coexistence domains between the condensed phase and the expanded one is clearly demonstrated, even at a very low concentration of impurities. Structural and morphological modifications during the polymerization where investigated using X-ray surface scattering together with atomic force microscopy. Whatever the polymerization conditions (constant area or constant pressure), X-ray reflectivity clearly shows the reorientation of the diacetylenic links. Only constant area polymerization leads to a viscoelastic behavior of the film, as shown by talcum decoration. The topochemical nature of the polymerization of diacetylenic groups induces strong constraints on the monolayers and, when the polymerization is achieved at constant area, leads to the collapse of the films evidenced by both techniques.

© Les Editions de Physique 1994